1. Field of the Invention
The present invention relates to a power transmission mechanism comprising a gear member formed with external gear teeth, an annular floating member formed with internal gear teeth meshed with the external gear teeth of the gear member, and arranged in an eccentric relation to the gear member, a transmission wheel member spaced from the floating member and the gear member, and an endless and flexible transmission member engaging the outer peripheries of the floating member and the transmission wheel member.
2. Description of the Prior Art
German Pat. No. 115,719 discloses a power transmission mechanism of the type mentioned above. With such a mechanism, the difference in tension of the endless transmission member between the tight side and slack side can be effectively compensated for. The term "endless transmission member" as used herein includes a cog-belt made of reinforced elastomeric material, and a chain. When the mechanism is used in a condition in which it is subjected to vibration, e.g. in a bicycle or the like, the floating member tends to laterally disengage from the gear member to such an extent that an efficient power transmission cannot be effected or, as the case may be, there takes place serious damage to the mechanism or to the frame of the bicycle or the like.
The occurrence of the lateral disengagement can be eliminated by providing the mechanism with a pair of guide plates for limiting the relative displacement between the gear member and the floating member. As described in German Offenlegungsschrift DE 31 00 922 A1 published after the priority date of the present application, those guide plates may be secured either to the gear member or to the floating member. On the other hand, provision of the guide plates encounters another problem that dust or foreign material tends to enter into the closed space between the internal teeth of the floating member and the external teeth of the gear member, through narrow gaps between the guide plates and the floating member and/or between the guide plates and the gear member. The gaps are more or less formed even when the guide plates are positively secured by bolts and nuts to the floating member or to the gear member, with their opposite inner sides in sliding contact with the outer sides of the gear member or the floating member, because of possible deformation or deflection of the guide plates accompanying an increase in sliding resistance between the guide plates and the gear member or floating member.